عنوان مقاله [English]
About 36 percent of Earth's land surface covered arid and semi-arid lands. 19 percent of these levels is dry completely and without plant life. In Iran, One-third to one-quarter of surfaces is covered with running sands (Ekhtesasi, 1375, 97).
So far, there has been a lot of discussion for identification of appropriate indicators for rapid assessment of Intensity and the extent of degradation in arid lands. Using of geomorphologic Indices Due to the It was possible to measure as a quantity and also it has a direct relationship to processes of erosion and sedimentation, is very important. Ripple mark Are waves that formed by the wind blowing on sandy areas. When wind blows on the sandy ground, Makes the movement of sand And therefore are formed Ripple marks (Montagne and Thomas, 2002, 806). Whatever Particle diameter is larger represents the region's severe winds, so larger particles is, more their resistance against wind erosion (welfare, 1388, 16).
Ghanei Bafghi and Yar Ahmadi) 1390) evaluated the relationship of sand dunes Aggregation With direction of erosive Wind In Hassan Abad Bafg Erg. The main objective of the plan is providing the index In addition to the existing indices to determine erosive Wind direction in the area that showed Erosive wind direction is Northern sector.
In Hassan Abad Bafg erg, It can be seen Two types of ripple mark One of them is small ripple mark That dispersed all over erg And other coarse Ripple marks That's just In between hills, In places where the wind due to Canalization Has High speed, For this study First, with the help of satellite images Investigated dune Has been determined And by visiting the study area has identified coarse Ripple marks (Figure 1).According to purpose of the study, Has been done Sampling from windward Slopes and leeward Slopes sediments of Ripple coarse marks.
This sampling as completely random and was conducted on 36 coarse ripple mark. These 1000g samples was held in plastic bags And for analysis was transferred to the laboratory. In the laboratory samples was passed a series of sieves 2, 1, 5/0, 25/0, 125/0, 063/0 mm, For 10 minutes, by shakers. Due to the Samples were without aggregate particles of all samples was sieve by. Dry method And Samples Weight measured in each sieve carefully.
The obtained data were inserted in the SPSS software and in order to assessment of Gradation difference in both Slopes of Ripple mark used t- test.
Results and discussion:
This research compares the Gradation Indices of windward and leeward slopes Particles coarse ripple marks in, Hasanabad Bafg erg. The results of Statistical Summary in Sample weight Showed that Particle diameter in windward slopes is greater than the leeward slopes. T-test results of sediments Weight in these two slopes showed that coarse ripple mark not significant. Particles Weight on the 2 mm sieve in confidence level of 5 percent, the rest of the particles weight on sieves 1, 5/0, 25/0, 125/0, 063/0 mm (Less than 2mm), were significant in confidence level of 5 percent; because it is the low weight of the particles. The results of t-test values d_10, d50, d90 Between the sediments Windward slopes and leeward slopes coarse ripple mark showed that At 5% level There is a significant difference between the two slopes sediments, Also, Because average of particles windward slopes Is greater than the leeward Slopes, Particle diameter windward Is Larger than the leeward.
According to folk formula and obtained information was observed particles of windward Slopes Has a high SORTING And particles of leeward Slopes has a weak Sorting.
The cause of which is Light sediment transport by the wind from windward Slopes and their associations in leeward Slopes and mixing of sediments in the area.
In the other words Due to particles carried from the windward Slopes Uniformity and SORTING In this area is more and due to Carried particles accumulation from the windward Slopes To leeward Slopes and mixture of particles Uniformity and particles of SORTING In this area is less. It can be concluded Particle diameter in windward Slopes Have more sorting to leeward and the results of t-test sorting according to Folk formula shows in Level of 99% there is significant differences among sediments.